Hello,
I'm new to the forum, and am glad there is a good source to get info on Outback questions! About a month ago, my check engine light came on, then went off, then came on again. I took it to a service shop and they said the code was for the knock sensor. I did not have them replace it at that time, but did start to notice the sluggishness and slow acceleration that I've read about when dealing with bad knock sensors. I did some research on the internet, and found that I could replace the sensor myself. However, I also found that sometimes all it takes is cleaning the sensor's contact with the engine to remedy the problem.
So, I removed the knock sensor, cleaned it with a brillo pad, cleaned the spot on the engine block where the sensor bolts in, and reinstalled the existing sensor. After that, the check engine light stopped coming off and on, and just STAYED on... this surprised me.
I decided the sensor must be bad, so I bought a replacement one at Napa and installed it this morning. The CEL is still staying on, and I'm not sure what the deal is. Does anybody know if it takes a while to turn off (assuming that installing the new sensor fixes the issue)? Or, does it turn off right away?

The CEL will stay lit for three full driving cycles after the offending part is replaced, as long as there are further symptoms. If no symptoms are experienced in three cycles, the light will go out on its own. However, the original code that caused it to come on (in this case the knock sensor) will remain in memory for up to 40 driving cycles (after which it too would be automatically erased).

By disconnecting the battery, the memory is being erased, and because it's clear, the CEL is also cleared. As long as the problem doesn't occur again, the light will remain out.

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